Patent GB-600040-A (GB)
Title: Photographic emulsions for colour photography
IPC: G03C7/388
Filed: 1945-08-24
Abstract: 600,040. Photographic emulsions. DU PONT DE NEMOURS & CO., E. I. Aug. 24, 1945, No. 21752. Convention date, Aug. 30, 1944. [Class 98 (ii)] Photographic emulsions are prepared by precipitating silver halide in an aqueous colloid solution (e.g. a gelatin solution), diluting, adding a small quantity of an anionic surface active agent, separating the silver halide from the colloid by centrifuging, and re-dispersing the silver halide in a hydrophilic colour-forming film-forming polymer or resinous condensation product. The surface active agent may be added to the aqueous solution used for dilution or may be added after dilution, and an additional quantity may be added to the silver salts prior to redispersion. The silver salts may be washed in the centrifuge with water. The gelatin emulsion may be ripened before ceiitrifuging, and may be formed using as the silver salt the nitrate, sulphamate, acetate, fluoride, phosphate, or citrate, and as the halide ammonium bromide, lithium bromide, potassium bromide, chloride, or iodide, sodium iodide or chloride, or ammonium iodide or chloride. The colloid may also be casein, albumen, agaragar, or gum arabic. Optical sensitizing dyes, sulphur sensitizers (e.g. allyl thiourea, allyl isothiocyanate, or sodium thiosulphate), and fog inhibitors may be added to the final emulsion. The colour-forming polymer or resinous condensation product may be derived from completely or partially hydrolysed polyvinyl esters (e.g. acetates, chloracetates, propionates, butyrates, or glycollates), completely or partially hydrolysed interpolymers of polyvinyl esters with polymerizable compounds (e.g. ethylene, propylene, butene-1, methyl and ethyl acrylates and methacrylates, vinyl chloride, vinyl cyanide, maleic anhydride, methyl vinyl ketone and the ethers and acetals of such compound), and alkyl resins containing a plurality of hydroxyl groups (e.g. sorbitolcitric acid resinous condensation products). The colour-forming nuclei may be attached to the resin by ester, carbonamide, sulphonamide, amino, imino, ester, or acetal linkages. Numerous colour-forming groups are specified. Resins specified are the reaction products of maminophenylmethylpyrazolone and vinyl chloride/maleic anhydride interpolymer, of 1:5- aminonaphthol and vinyl chloride/maleic anhydride interpolymer, of 1-phenyl-3-methyl-5- pyrazolone carboxylic acid and polyvinyl maminobenzal, and of acetoacetaminophenylcarboxylic acid and polyvinyl m-aminobenzal. The surface-active substance may be an alkalimetal, ammonium, or amine salt of a primary or secondary monoalkyl sulphate or sulphonic acid or a cycloaliphatic sulphonic acid of 8 to 18 carbon atoms or of an alkyl-substituted naphthalenesulphonic acid or aldehyde condensation product thereof or of a saturated or substantially saturated aliphatic carboxylic acid of 10 to 24 carbon atoms. In example 1, gelatin silver bromide emulsion is diluted with aqueous sodium dodecylsulphate solution and is centrifuged, washed, and recentrifuged. The silver bromide obtained is mixed with aqueous caustic soda solution of the mixed acetal of polyvinyl alcohol with salicylaldehyde and osulphobenzaldehyde. The resultant dispersion is coated on to a cellulose derivative support, and after exposure is colour developed, washed, and the silver removed by bleaching and fixing. In example 2, an ammoniacal silver nitrate solution and a mixed ammonium bromidepotassium iodide solution, both containing diethylcyclohexylamine dodecylsulphate, are simultaneously added to an aqueous gelatin solution, the emulsion is diluted and centrifuged, the silver halide is washed with dilute aqueous diethylcyclohexylamine dodecylsulphate, washed with water, and re-centrifuged, and an aqueous paste of the silver halide containing diethylcyclohexylamine dodecylsulphate is added to an aqueous-ethanol solution of symmetrical bis-[m-(3-methyl-5-pyrazolone-1- yl)phenyl]-urea-formaldehyde condensation product and caustic soda. The emulsion obtained may be coated on a cellulose acetate support. In example 3, the procedure is similar, but the paste is added to an aqueous-caustic soda solution of the mixed acetal of polyvinyl alcohol with allylsalicylaldehyde and phthalaldehydic acid containing dimethyl formamide. The resultant emulsion may be coated on to a cellulose acetate or baryta-coated paper support. The dispersions may be used in the preparation of three-layer colour photographic material. Specifications 376,746, 479,838, 489,161, 513,471, 519,895, 535,341, 537,961, 593,088, 598,367, 598,475 and 600,023 are referred to.